• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.4
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• pp.99-105
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• 1999

The flatness is the most important nature for the surface plates. For finding such a flatnes a surface plate is surveyed along a number of straight lines parallel to the edges of plate which form a grid pattern. Next the variations in height of the grid points are measured relative to a datum point. the relation between the number of such grid points and the flatuness of a measured surface plate is formulated in this study. In addtion it is found that the grid-point-numbers suggested by KS B 5254 and JIS B 7513 have very poor reliability for estimation of flatness incase of the surface plates with poor original flatness.

• The Journal of the Korea Contents Association
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• v.5 no.1
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• pp.189-199
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• 2005

The grid computing is a technique to solve big problems such as a field of scientific technique by sharing the computing power and a big storage space of the numerous computers on the distributed network. The environment of the grid computing is composed with the WAN which has a different performance and a heterogeneous network condition. Therefore, it is more important to reflect heterogeneous performance elements to calculation work. In this paper, we propose an efficient method that decides work process number of each node by considering a network state information. The network state information considers the latency, the bandwidth and latency-bandwidth mixture information. First, using information which was measured, we compute the performance ratio and decide work process number of each node. Finally, RSL file was created automatically based on work process number which was decided, and then accomplishes a work. The network performance information is collected by the NWS. According to experimental results, the method which was considered of network performance information is improved respectively 23%, 31%, and 57%, compared to the methods of existing in a viewpoint of work amount, work process number, and node number.

• Structural Engineering and Mechanics
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• v.70 no.3
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• pp.279-287
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• 2019

This paper intends to introduce a near-tip grid refinement and to explore its usefulness in the crack analysis by the natural element method (NEM). As a sort of local h-refinement in FEM, a NEM grid is locally refined around the crack tip showing the high stress singularity. This local grid refinement is completed in two steps in which grid points are added and Delaunay triangles sharing the crack tip node are divided. A plane-state plate with symmetric edge cracks is simulated to validate the proposed local grid refinement and to examine its usefulness in the crack analysis. The crack analysis is also simulated using a uniform NEM grid for the sake of comparison. The near-tip stress distributions and SIFs that are obtained using a near-tip refined NEM grid are compared with the exact values and those obtained using uniform NEM grid. The convergence rates of global relative error to the total number of grid points between the refined and non-refined NEM grids are also compared.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.24 no.1
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• pp.1-22
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• 2020

An accurate and efficient gradient estimation method on unstructured grid is presented by proposing a switching process between two Least-Square methods. Diverse test cases show that the gradient estimation by Least-Square methods exhibit better characteristics compared to Green-Gauss approach. Based on the investigation, switching between the two Least-Square methods, whose merit complements each other, is pursued. The condition number of the Least-Square matrix is adopted as the switching criterion, because it shows clear correlation with the gradient error, and it can be easily calculated from the geometric information of the grid. To illustrate switching process on general grid, condition number is analyzed using stencil vectors and trigonometric relations. Then, the threshold of switching criterion is established. Finally, the capability of Switching Weighted Least-Square method is demonstrated through various two- and three-dimensional applications.

• Journal of Environmental Impact Assessment
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• v.19 no.5
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• pp.465-473
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• 2010

This study was carried out to investigate the effect of EFDC hydrodynamic result on the WASP7.3 water quality modeling result in accordance with the change of number of grid for the dam reservoir to be constructed. The simulated flow and BOD, T-N and T-P loads by the HSPF watershed model was used for boundary conditions and the hydrodynamic modeling results was linked with WASP model to predict future water quality after dam construction. The scenarios for EFDC modeling were composed of Scenario 1(141 grid cells) and Scenario 2(568 grid cells). The results of Scenario 2 showed that BOD, T-N, T-P and Chl-a concentrations were decreased 0.073mg/L(8.5%), 0.032mg/L(2.6%), 0.003mg/L(6.8%), 0.644mg/L(4.2%) compared with those of Scenario 1, respectively. As number of grid cell increased, water quality concentrations were decreased and also it caused the longer running time. Therefore, this study suggests that the consideration of the geometry of water body is more important than the number of grid cells for the prediction of water quality of a dam reservoir in EIA.

• Fire Science and Engineering
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• v.23 no.1
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• pp.1-6
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• 2009

The aim of this study is to analyse the sensitivity of fire simulation parameters including grid size and solid angle number which affect the performance of subway cabin fire simulation by FDS 4.07 version. The results of sensitivity analysis shows average of $10{\sim}20%$ differences in plume temperature, upper layer temperature, and layer height depending on the change of grid size. The study also shows that simulation with 0.05m grid size produces better resolution than that with coarse one which is 0.1m.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.419-425
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• 2014

The current work investigated the variation of numerical solutions according to the grid number, the distance of the first grid point off the ship surface, turbulence modeling and discretization. The subject vessel is KVLCC. A commercial code, Gridgen V15 and FLUENT were used the generation of the ship hull surface and spatial system and flow computation. The first part of examination, the effect of solutions were accessed depending on the grid number, turbulence modeling and discretization. The second part was focus on the suitable selection of the distance of the first grid point off the ship surface: $Y_P+$. When grid number and discretization were fixed the same value, the friction resistance showed differences within 1 % but the pressure resistance showed big differences 9 % depending on the turbulence modeling. When $Y_P+$ were set 30 and 50 for the same discretization, friction resistance showed almost same results within 1 % according to the turbulence modeling. However, when $Y_P+$ were fixed 100, friction resistance showed more differences of 3 % compared to $Y_P+$ of 30 and 50. Whereas pressure resistance showed big differences of 10 % regardless of turbulence modeling. When turbulence modeling and discretization were set the same value, friction, pressure and total resistance showed almost same result within 0.3 % depending on the grid number. Lastly, When turbulence modeling and discretization were fixed the same value, the friction resistance showed differences within 5~8 % but the pressure resistance showed small differences depending on the $Y_P+$.

• Journal of Korean Society for Quality Management
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• v.49 no.2
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• pp.201-211
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• 2021

Purpose: This paper proposes a density adaptive grid algorithm for the k-NN regression model to reduce the computation time for large datasets without significant prediction accuracy loss. Methods: The proposed method utilizes the concept of the grid with centroid to reduce the number of reference data points so that the required computation time is much reduced. Since the grid generation process in this paper is based on quantiles of original variables, the proposed method can fully reflect the density information of the original reference data set. Results: Using five real-life datasets, the proposed k-NN regression model is compared with the original k-NN regression model. The results show that the proposed density adaptive grid-based k-NN regression model is superior to the original k-NN regression in terms of data reduction ratio and time efficiency ratio, and provides a similar prediction error if the appropriate number of grids is selected. Conclusion: The proposed density adaptive grid algorithm for the k-NN regression model is a simple and effective model which can help avoid a large loss of prediction accuracy with faster execution speed and fewer memory requirements during the testing phase.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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• pp.128-134
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• 2005

In the CFD area, the numerical analysis of high Mach number flow over a blunt-body poses many issues. Various numerical schemes have been developed to cover the issues, but the traditional schemes are still used widely due to the complexities of new schemes and intricacy of modifying the established codes. In the present study, the well-known Roe's FDS based on TVD-MUSCL scheme is used for the solution of very high Mach number three-dimensional flows posing carbuncle and non-physical phenomena in numerical analysis. A parametric study was carried out to account for the effects of the entropy fixing, grid configurations and initial condition. The carbuncle phenomena could be easily overcome by the entropy fixing, and the non-physical solution could be eliminated by the use of the modified initial condition regardless of entropy fixing and grid configurations.

• Journal of Positioning, Navigation, and Timing
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• v.2 no.1
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• pp.59-65
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• 2013

The signal broadcast from a GPS satellite experiences code delay and carrier phase advance while passing through the ionosphere, which causes a signal error. Many ionosphere models have been studied to correct this ionospheric delay error. In this paper, the ionosphere modeling for the Korean Peninsula was carried out using a spherical harmonics based model. In contrast to the previous studies, we considered a real-time ionospheric delay correction model using fewer number of basis functions. The modeling performance was evaluated by comparing with a grid model. Total number of basis functions was set to be identical to the number of grid points in the grid model. The performance test was conducted using the GPS measurements collected from 5 reference stations during 24 hours. In the test result, the modeling residual error was smaller than that of the existing grid model. However, when the number of measurements was small and the measurements were not evenly distributed, the overall trend was found to be problematic. For improving this problem, we implemented the modeling with additional virtual measurements.